When a shoulder-held firearm is discharged, a rearwardly directed recoil force is generated as a result of the force impulse created to accelerate the ammunition. This recoil imparts a load on the shoulder of the shooter which is not only uncomfortable, but over repeated firings can lead to fatigue of the shooter. Various energy absorption devices have heretofore been used in connection with firearms to dissipate the recoil energy produced upon discharge of the firearm. In one class of energy absorption devices heretofore proposed for use in reducing recoil impact, a recoil assembly is disposed in the firearm stock rearwardly of the bolt and carrier assembly.
For example, U.S. Pat. No. 3,977,296 discloses a hydraulic buffer assembly in a fixed stock automatic or semiautomatic firearm for providing a reduced rate of fire and a mild recoil shock reduction. The disclosed hydraulic buffer assembly is axially translatable within the receiver extension tube and includes a piston and a pair of fluid-filled chambers interconnected by a fixed orifice passage. The receiver extension tube is threaded at its forward end into the gun receiver, extends rearwardly in a cavity in the stock of the firearm and is secured at its aft end to the butt end of the stock. The hydraulic buffer assembly is in coaxial alignment with the bolt and carrier assembly with the rearward end of the bolt and carrier assembly contacting the forward end of the piston of the hydraulic buffer assembly. In operation, when the firearm is discharged, the expanding gases drive the bolt and carrier assembly and the buffer rearwardly in unison against a first coil spring disposed within the buffer assembly. The bolt and carrier assembly also drives the buffer assembly rearward against a second coil spring disposed about the exterior of the buffer assembly until the rearward end of the buffer strikes the butt end wall of the receiver extension tube. Hydraulic resistance commences as soon as the piston is displaced as fluid passes from one chamber to the other chamber through the fixed orifice passage. These hydraulic buffer assemblies are only useable in weapons that allow the bolt and carrier assembly to move within the receiver extension tube.
U.S. Pat. No. 4,164,825 discloses a device for reducing firearm recoil on a shoulder-fired firearm wherein the recoil energy absorption device is mounted within a fixed gun stock. The device disclosed therein includes a tubular case defining an elongated interior chamber filled with a viscous liquid and housing a vaned piston disposed between a reset spring and a reset damper spring. The device is inserted in an elongated cavity drilled in the gun stock and extending substantially parallel to the gun barrel. When the firearm is fired, the recoil energy is dampened as the case and liquid therein are driven rearwardly against the resistance of the piston.
U.S. Pat. No. 5,410,833 discloses a recoil absorbing firearm stock utilizing a stacked arrangement of cupped-discs to decrease the impact force felt by the individual firing a shoulder-fired firearm. The disclosed recoil absorbing stock includes a buttstock and a stock grip interconnected by a telescoping stabilizing strut and an adjustable length recoil absorbing strut disposed in parallel. The recoil absorbing strut includes a plurality of compressible, cupped-disc springs arranged in nested sets and mounted on a guide rod for absorbing the recoil energy produced upon discharge of the firearm. The compressive preload on the stack of nested sets of cupped-disc springs may be adjusted by turning a tensioning screw.
A collapsible buttstock for use on shoulder-held firearms having a built-in recoil shock absorber is commercially available under the product name “Stock Shox”. The recoil shock absorber inside the buttstock includes a compression-rebound unit of the type disclosed in U.S. Pat. No. 5,888,214. The compression-rebound unit includes a housing, a cylindrical resilient elastomeric body mounted in the housing for compression and post-compression expansion, and a displacement member extending into the housing. In response to recoil generated upon discharge of the firearm, the displacement member moves rearward within the housing compressing the resilient elastomeric body. Upon completion of the rearward stroke, the elastomeric body expands and returns the displacement member to its original position.